RFI testing can be broken down into two categories, the testing of how electronic equipment is susceptible to external RF sources, and the testing of the RF noise emitted by electronic equipment during its operation. For the latter, testing can comprise placing the equipment in an anechoic chamber and detecting RF using a receiving antenna at different positions and orientations with respect to the equipment. This allows the emissions to be characterized. For the former, susceptibility to RF interference typically depends on the orientation of the RF field as well as the frequency. Such testing can comprise using an RF reflective chamber, called a reverberation chamber, and varying the amplitude and phase of the RF field. The most common way to create such variation is to place a stirrer within the reverberation chamber. The stirrer is a large metal “paddle” or undulated metal sheet that is rotated to cause the RF energy to be reflected into a variety of different modes within the chamber. When a stirrer is not used, a source can be positioned differently to create different modes within the chamber. This is typically done by placing the RF source in a first position, taking measurements or testing performance of the electronic device, and then repeating with different RF source positions or orientations.
In the case of aircraft, the fuselage is often made of aluminum and creates an RF reflective chamber. RF emitters, such as WiFi and mobile telephone transmitters, can result, in particular when a large number are involved, in significant RF power being generated within the chamber of the fuselage. Testing of the impact of such RF power on cockpit equipment is known in the art.
When testing susceptibility, it is desirable to provide RF power for each frequency, with each orientation, with each polarization, and at consistent power. Practically, this is difficult to achieve. Physically moving a source to assume every orientation and polarization around equipment to be tested in an anechoic chamber is onerous. In the case of an aircraft where testing of installed cockpit equipment is to be done, moving the source around the equipment to be tested is not possible. Ensuring that each orientation and polarization of the RF source will impinge on the equipment to be tested in a chamber not having a stirring paddle is a challenge.
In US patent pre-grant publication 2009/030141 (published on 10 Dec. 2009, naming assignee EADS France), a reverberation chamber is disclosed that has an RF transmitter whose azimuth and elevation are controlled by motorized drives. As described in this reference, the aim of the reverberation chamber system is not to provide for electromagnetic excitation distributed in every direction with the same power but rather, at the position of the object 12, to foresee stresses applied this object 12 along the greatest possible variety of angles of incidence, (preferably an exhaustive range of angles of incidence and with significant power) and good statistics less dependent on the characteristics of the chamber. The disclosed embodiments, by causing the source to rotate and the stirrer to rotate about the source, creates a stirring that is simultaneously mechanical and positional. However, with the disclosed embodiments, ensuring that the equipment to be tested receives RF power at every angle of incidence and at every polarization requires either a stirring device and/or special control over the geometry of the test system.